In this work, the MgO-CO2 working pair has been adapted for thermochemical energy storage (TCES) at medium temperatures by the MgO modification with inorganic salts to promote the TCES dynamics. Brief screening of modifying salts showed that lithium acetate (LiOAc) and mixed lithium-potassium nitrate (Li0.42K0.58NO3) additives could considerably promote the MgO carbonation at P(CO2) <= 10 bar and T >= 300 degrees C. The de- and re-carbonation kinetics, as well as cycling stability of the doped MgO/MgCO3, was reported to outline possible TCES operating conditions (T = 280 degrees C-380 degrees C, P(CO2) = 0-1 bar). The heat storage capacity of the salt-promoted MgO was estimated to be 1.6 GJ/m(3). A concept of chemical heat pump utilizing the MgO-CO2 working pair was discussed. The salt-promoted MgO-CO2 working pair was concluded to be promising for TCES.